"First the woman smiles at her admirer and lifts her eyebrows in a swift, jerky motion as she opens her eyes wide to gaze at him. Then she drops her eyelids, tilts her head down and to the side, and looks away. Frequently she also covers her face with her hands, giggling nervously as she retreats behind her palms.

"This sequential flirting gesture is so distinctive that [German ethologist Irenaus] Eibl-Eibesfeldt was convinced it is innate, a human female courtship ploy that evolved eons ago to signal sexual interest."

2/

Look for someone 'in your league'

Men — and women — are attracted to people who are as attractive as they are.

In one study, researchers at the University of California at Berkeley looked at the behavior of 60 heterosexual male and 60 heterosexual female users on an online dating site. While the majority of users were inclined to reach out to highly attractive people, they were most likely to get a response if that person was about as attractive as they were (as judged by independent raters).

"If you go for someone roughly [equal] to you in attractiveness, it avoids two things," Nottingham Trent University psychologist Mark Sergeant, who was not involved with the study, told The Independent. "If they are much better-looking than you, you are worried about them going off and having affairs. If they are much less attractive, you are worried that you could do better."

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Present yourself as high status

AP/Laurent Cipriani

A 2010 study from the University of Wales Institute found that men pictured with a Silver Bentley Continental GT were perceived as way more attractive than those pictures with a Red Ford Fiesta ST.

And a 2014 study from Cardiff Metropolitan University found that men pictured in a luxury apartment were rated more attractive than those in a control group.

Interestingly, men don't seem to be more attracted to women when they're pictured in a high-status context.

"We think this suggests greater financial independence gives women more confidence in partner choices, and attracts them to powerful, attractive older men," lead author and University of Dundee psychologist Fhionna Moore said in a statement.

Evolutionary psychologists say that younger women and older men often pair up because while fertility only lasts from puberty to menopause in women, it can extend long into midlife for many men. Society also gives men greater opportunity to accumulate status and resources as they age.

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Grow a light beard

Larry Marano / Getty

In a 2013 study from researchers at the University of New South Wales, researchers had 177 heterosexual men and 351 heterosexual women look at images of 10 men in one of four conditions: clean-shaven, light stubble, heavy stubble, or full beard. Participants rated the men pictured on several traits, including attractiveness.

Results showed that women were more likely to want short-term relationships with the guys who had big muscles.

The evolutionary signal that might be at work here?

Characteristics like muscularity are "cues of genes that increase offspring viability or reproductive success," say authors David A. Frederick and Martie G. Haselton.

But Frederick and Haselton took away another telling finding: Less-muscular men were thought to be a better fit for long-term relationships. So if you want to catch a woman's eye and hold her attention, you may be better off not going overboard.

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Be kind

Rommel Demano / Getty

One of the best documented findings in psychology is the halo effect, a bias where you unconsciously take one aspect of somebody as a proxy for their overall character. It's why we think beautiful people are good at their jobs, even when they aren't necessarily.

In a 2014 Chinese study, more than 100 young people looked at images of men and women's faces and rated them on attractiveness. Each face pictured was paired with a word that described either a positive personality trait — like kindness or honesty — or a negative personality trait, like being evil or mean.

Results showed that the people described with positive traits were rated more attractive.

"Even though beauty is an assessment of fitness value, there is no reason why assessment of fitness needs to be purely physical," Kaufman writes, meaning that acting kind can make you appear more attractive.

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Wear red

Mike Coppola / Getty

A 2010 cross-cultural study— with participants from China, England, Germany, and the US — found that women are most attracted to men wearing red.

In one experiment from the study, 55 female undergrads looked at a color photo of a man in either a red or green shirt, and then rated the man's attractiveness.

Sure enough, the man was rated significantly more attractive when he was wearing a red shirt. The results were similar when researchers compared the red shirt to other color shirts as well.

Interestingly, participants generally weren't aware that the man's clothing color was influencing their perceptions of his attractiveness.

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Make your partner laugh

Multiple studies indicate that women are more attracted to men who can make them laugh. Interestingly though, men generally aren't more attracted to women who can make them laugh.

In one 2006 study published in the journal Evolution and Human Behavior, researchers asked undergraduate students (they didn't indicate their sexual orientation) to indicate how much they valued a partner's ability to make them laugh and their own ability to make their partner laugh.

Results showed that women valued both their partner's sense of humor and their own ability to make their partner laugh; men valued only their own ability to make their partner laugh.

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Walk a dog

In a 2014 experiment from the Ruppin Academic Center in Israel and the University of Michigan, 100 Israeli women read vignettes about men.

Some of the men were described as "cads": They would cheat on their partner and get into fights. The other men were described as stereotypical "dads": They would work hard at their job and take good care of their kids.

Whenever the story featured a cad who owned a dog, women rated that man as a more suitable long-term partner than a cad who didn't own a dog. Cads with dogs were even rated slightly more attractive than dads with dogs.

The researchers concluded that owning a pet signals that you're nurturing and capable of making long-term commitments. It can also help you appear more relaxed, approachable, and happy.

After each interaction with an opposite-sex partner, students privately indicated how "sexy" they found their partner and how much they'd like to date that person.

Results showed that men were generally more drawn to physically attractive women. (Independent coders had rated the students' attractiveness beforehand.) But women were generally more attracted to mindful men.

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Play extreme sports (carefully)

A 2014 study led by researchers at the University of Alaska at Anchorage found that women are attracted to men who take what the researchers call "hunter-gatherer risks."

More than 230 undergrads filled out questionnaires about how attractive they would find a partner who engaged in certain risky behaviors, as opposed to a partner who engaged in low- or no-risk behaviors.

Hunter-gatherer risks included mountain biking, deep-sea scuba diving, and extreme rollerblading. "Modern" risks included plagiarizing an academic paper, casually handling chemicals in a lab, and not updating the virus-protection software on your computer.

Low- and no-risk behaviors included biking along paved paths and carefully handling chemicals in a chemistry-lab class.

Results showed that women said they would be more attracted to men who engaged in hunter-gatherer risks — the kinds that were similar to risks faced by ancestral humans. Women said they would be less attracted to men who engaged in modern risks, which might seem just plain dumb.

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Wear a scented deodorant

Simply knowing that you're wearing a new fragrance can make you act more confident, and even make you seem more attractive to other people.

In a small 2009 study published in the International Journal of Cosmetic Science, researchers gave one group of male undergraduates a spray with antimicrobial ingredients and fragrance oil, and provided another group with an unscented spray that didn't contain antimicrobial ingredients. Over the next few days, the men who used the scented spray reported higher self-confidence and felt more attractive.

The strange part? When a group of women were shown silent videos of the men, they found those who were wearing scented spray more attractive, even though they obviously couldn't smell them. The researchers determined that the men using the scented spray displayed more confident behavior, which in turn made them more attractive.

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Chow down on garlic

The smell of garlic on your breath is generally regarded as an instant romance killer. But a recent series of studies, from researchers at Charles University and the National Institute of Mental Health in the Czech Republic and the University of Stirling in the United Kingdom, suggests a different story when it comes to body odor.

In one study, eight men ate a slice of bread with cheese and 12 grams of fresh garlic; another eight ate bread and cheese without any garlic. For the next 12 hours, the men wore cotton pads under their armpits and were instructed not to use any deodorants or fragrances.

The following day, all the men returned to the lab, where 40 women sniffed the pads and rated the odor on pleasantness, attractiveness, masculinity, and intensity. Results showed that the garlic group was rated more pleasant and attractive and less masculine and intense.

16/

Do volunteer work

About 30 women looked at a picture of a man with a brief description of his hobbies, which sometimes included volunteer work. The same procedure was repeated with about 30 men looking at a picture of a woman. Everyone rated how attractive they found the person pictured for a short- and long-term relationship.

Both genders rated the person pictured as more attractive for a long-term relationship when they were described as a volunteer — but the effect was stronger for women rating men.

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Show off your scars

Warner Bros. Pictures/YouTube

That scar on your chin from when you fell off a bike could help you attract a mate.

In a 2009 study, researchers at the University of Liverpool and the University of Stirling took photos of 24 male and 24 female undergrads. They digitally manipulated half of the images so the subjects appeared to have facial scars — for example, a line on the person's forehead that looked like the result of an injury.

Then the researchers recruited another group of about 200 heterosexual male and female undergrads to rate all the people pictured based on attractiveness for both short- and long-term relationships.

Results showed that men with scars appeared slightly more attractive for short-term relationships than men without scars. Women, on the other hand, were perceived as equally attractive regardless of whether they had scarred faces.

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Use open body language in your online dating photo

Getty/Cindy Ord

A 2016 study— from researchers at the University of California, Berkeley, Stanford University, the University of Texas at Austin, and Northwestern University — suggests that we're more attracted to people who display expansive body language.

In one experiment included in the study, the researchers created profiles for three men and three women on a GPS-based dating app.

In one set of profiles, the men and women were pictured in contractive positions — for example, by crossing their arms or hunching their shoulders.

In the other set of profiles, the same men and women were pictured in expansive positions, like holding their arms upward in a "V" or reaching out to grab something.

Results showed that people in expansive postures were selected as potential dates more often than those in contractive postures. This effect was slightly larger for women selecting men.

Look proud

In one experiment included in the study, researchers had nearly 900 North American adults look at photos of opposite-sex individuals online.

The researchers were specifically comparing people's perceptions of expressions of pride, happiness, shame, and neutrality (other people had already identified the emotion behind the expression in the photo). For women evaluating men, the most appealing expression was pride, and the least appealing was happiness.

Even weirder, an expression of shame was relatively attractive on both men and women.